Manufacture of crotonaldehyde from acetaldehyde and aldol



Patented Dec. 4, 1928.

UNITED STATES PATENT-OFFICE.

EMIL LuscnEa, or BASEL, swrrzERLANn, .essrenoa TO THE cor/tram; nnnxrnrzrm'rswaax LONZA, or AMPEL AND BASEL, SWITZERLAND.

MANUFACTURE OF CROTONALDEHYDE FROM ACETALDEHYDE AND ALDOL.

1T0 Drawing. Application filed April 25,' 1927, Serial No. 186,591, and in Switzerland Maya, 1926.

In the technical manufacture of crotonaldehyde there was hitherto used aldol which in its turn was obtainedby treating acetaldehyde with alkaline reacting substances. The 5 output in this manufacture was not quite what .one could wish, as in the aldolizing operation as well as in the distillation greatly disturbing secondary reactions are produced. In the processes hitherto disclosed for the 1.0 preparation of aldol, reaction mixtures were formed, which according to the nature of the used condensating agents required a separation of the pure aldol from the solid salts ,oraqueous solutions, an operation which was l5 somewhat expensive owing to the great v1scosity of .the aldol and higlierresin like condensation products. If the crude aldol thus obtained 'is not purified, it is not adapted for the direct preparation of crotonaldehyde 20 for the reason thatgthe salts which are pres ent in solidpr dissolved form have a disturb-- ing action on the distillation inasmuch as they cause the formation of a resinous prodnot, thus diminishing considerably the output and more. 7

Now, it has been found that in the manufacture of crotonaldehyde from acetaldehyde and a-ldol these drawbacks can be avoid- 30 ed if acct-aldehyde is combined in an atmosphere of'initrogen with only such a quantity of a diluted aqueous solution of a caustic alkali that subsequent neutralization of. the

product of reaction by a mineral acid does not I cause precipitation, and if after addition ofa mineral acid the reaction mixture containing aldol, acetaldehyde and a little salt is fractionally distilled without previous purification or separation, within a circulating 4O atmosphere of nitrogen.

The quantity of a-lkali'hydroxide, which is i used in the present case, isonly about 1 to 2 hundredth per cent of the weight of acetaldehyde when in form of a diluted watery solu- 450 tion. The advantages of such a weak alkali concentration consist in that first an extreme- 1y pure aldol, that is one which contains only traces of higher condensation products is formed, that secondly no precipitation is produced on the neutralization with a mineral acid, such as for example sulfuric acid or phosphoricacid, and that thirdly this weak salt concentration does not afiect unfavorably the distillation or thetransformation of the aldol to crotonaldehyde.

losses which may attain to per cent .When' the distillation is conducted in a continuous way, outputs of crotonaldehyde are obtained, which may be of 95 to 98 per cent of the theoretical value. If the operation takes place in this manner, the isolation of the aldol in pure state is not necessary.

If the solution of the alkalihydroxide is caused to run directly into great quantities of water-free acct-aldehyde a great heating of the mass takes place'at'the beginning, which shouldbe conveniently moderated by an outer cooling. If, however, the alkali solution is .caused to run into a mixture of acetaldehyde and aldo-l, thereaction tempera ture can easily be maintained for example at to 40 0., provided that acetaldehyde is cplriitinuously added simultaneously with the a a 1.

The following example il'lustratesthe improved process:

100 kg. of acetaldehyde are mixed in an atmosphere of nitrogen little by little with 200 cms of a .5 per cent solution of sodium hydroxide, whereby the temperature is allowed to rise slowly to about 30 to 85 C.

' After the addition of all of the alkali, the reaction mixture is still'left for some time at this-temperature.v To the reaction. mixture there is then added 1 kg. of phosphoric acid and a fractional distillation is performed in a circulating atmosphere of nitrogen. ere operating in this manner, crotonaldehyde is obtained in a. good output.

The operation is effected in an atmosphere of nitrogen for the reason that acetaldehyde, for example when being stirred, very easily absorbs oxygen which gives rise to the formation of acetic acid, whereby the condensation would be unfavorably affected.

' In the manufacture of aldol from acetaldehyde there was hitherto employed alkaline condensing agents in quantities of 0,5% and more. The use of such considerable quantities of alkalis causes, however, on the neutralization of the alkali bya mineral acid a separation of salts which on the further treatment of the ald'ol have an interfering or resinating action. p

Instead of phosphoric acid sulfuric acid or 1 any other convenient mineral acid can be used.

What I claim is:

A process for the manufacture of crotonaldehyde from acetaldehyde and aldo-l, conmosphere of nitrogen with only such a quanof a diluted aqueous solution of a caustic alkali asto not cause any precipitation on subsequent neutralization, then adding a tity 5 mineral acid to the reaction product to obtain a reaction mixture acetaldehyde and a'little sacont-aining aldol.

1t, and finally dis EMIL LUsoHER.

atmosphere of nitrogen. 10 

